The invention relates to rod forming machines of the tobacco processing industry in general, and more particularly to improvements in wrapping mechanisms (also called sizing parts) of such machines. Typical examples of rod forming machines of the tobacco processing industry which employ wrapping mechanisms are machines which convert a stream of tobacco particles into a continuous cigarette rod and machines which convert a stream of fibrous filter material into a continuous filter rod.
The invention will be described with reference to the wrapping mechanism of a cigarette rod making machine. However, it is to be understood that the wrapping mechanism which embodies the present invention can be used with equal advantage in machines which are designed to turn out cigarillos, cigars, filter rod sections or any other rod-shaped articles of the tobacco processing industry wherein a substantially cylindrical filler of tobacco or other fibrous material is surrounded by a wrapper of cigarette paper, imitation cork and other flexible strip-shaped wrapping material.
The wrapping mechanism of a cigarette rod making machine normally comprises a substantially channel-shaped member which cooperates with a so-called tongue to define a path for the travel of an elongated reach or stretch of an endless belt conveyor, known as garniture tape or garniture belt which serves to drape the web of cigarette paper or other suitable wrapping material around a continuous rod-like filler of natural tobacco, artificial tobacco, reconstituted tobacco or a mixture of several fibrous materials. The channel-shaped member has a guide surface which is designed in such a way that successive increments of the aforementioned reach or stretch of the garniture tape continuously undergo gradual deformation so that a flat portion of the stretch is converted into a substantially U-shaped body which surrounds the web of wrapping material at three sides in order to partially convert the originally flat web of wrapping material into a tube. As a rule, one marginal portion of the unfinished tube extends outwardly and away from the other marginal portion so that it can be coated with a suitable adhesive prior to bonding it to the other marginal portion. The marginal portions form the customary seam which extends in parallelism with the longitudinal axis of the resulting cigarette rod. The rod is subdivided into plain cigarettes of unit length or multiple unit length during travel through a cutter known as cutoff.
A drawback of conventional wrapping mechanisms (sizing parts) of cigarette rod making and other machines of the tobacco processing industry is that the shaping of the aforementioned guide surface on the channel-shaped member requires a substantial amount of work in a complex machine which must be operated by a skilled artisan. As a rule, the guide surface is configurated in such a way that it resembles the letter V whose legs define a relatively large angle at the inlet end of the wrapping mechanism. The legs gradually slope toward each other so as to reduce the angle therebetween. The cross-sectional outline of the guide surface at the outlet end of a conventional channel-shaped member resembles the letter U. Such guide surface can be said to consist of a large number of relatively short surfaces extending substantially tangentially of the cylindrical peripheral surface of the filler which is caused to travel through the wrapping mechanism. Otherwise stated, the individual short surfaces which together constitute the guide surface of a conventional channel-shaped member extend substantially helically of a cylinder with a radius corresponding to the radius of the cigarette rod which issues when the wrapping mechanism. The making of the guide surface is a complex, tedious, and time-consuming procedure. Furthermore, it is not possible to produce two or more guide surfaces of identical or practically identical shape.